This invention is primarily applicable to materials such as Bauxites and Clays that have present as major impurities iron and titanium in various mineral forms.
There has been a great deal of research and there is a vast quantity of literature in attempts to produce a relatively iron-free alumina, alumina-silica product and aluminum chloride from such raw materials as Bauxites and Clays. None of the processes proposed have been shown to be economically successful.
This problem can best be described by the following references: Landsberg "Chlorination Kinetics of Aluminum Bearing Minerals:" Metallurgical Transactions B, Volume 6B, June 1975; pps. 207-208. To quote from page 208, 1st column:
"Whereas Foley and Tittle showed that iron could be removed from pre-reduced bauxite by chlorination to produce a refractory grade alumina, FIG. 2 indicates that a substantial loss of alumina accompanies the initial rapid iron chlorination under reducing conditions. Even if this loss could be tolerated the remaining iron is too high for producing cell grade alumina or aluminum chloride." PA1 "In general, the reduction of aluminum-containing materials with chlorine in the presence of reducing carbon in some form to produce aluminum chloride is an old and generally well-known reaction and one of the suggested expedients referred to above utilized Bauxite as the alumina containing material. Bauxite however, normally contains many impurities including iron oxide, silica, and titania. Since these impurities readily react with chlorine in the presence of carbon to form iron, silicon, and titanium chlorides, the usual gaseous aluminum chloride reaction effluent therefrom must be subjected to cumbersome and expensive after-purification measures if these chloride contaminants are to be separated to provide even a reasonably pure aluminum product." PA1 "The raw materials that may be used for the preparation of AlCl.sub.3, include bauxite, clays, shale, anorthosite, coal ash, and many other aluminum containing materials. Bauxite or clays are the most logical choices because of their higher Al.sub.2 O.sub.3 contents and the large reserves of these materials available. Iron is the impurity most deleterious to the process since it uses up chlorine and is difficult to remove from the product." PA1 "It is true that when processing between 900.degree. C.-1150.degree. C. titanium is removed from the original material along with the iron in the form of titanium tetrachloride, but only in small amounts unless a large excess of aluminum chloride is used." PA1 "(b) Excess AlCl.sub.3 that is used is recovered at a low cost as an impure AlCl.sub.3 containing FeCl.sub.3 and returned to the Number One Chlorination Stage without any deleterious effects on chlorinating the contained iron and titanium minerals."
U.S. Pat. No. 3,842,163, A. S. Russell et al, entitled "Production of Aluminum Chloride" and assignors to Aluminum Company of America, state, to quote lines 45 to 58:
The U.S. Department of the Interior, Information Circular i412 by Robert L. de Beauchamp, sums up the problem of producing AlCl.sub.3 from various materials on page 6, the last paragraph reading as follows:
Canadian Pat. No. 569,830 to Groth in 1939 described a method for chlorinating aluminiferous materials by treating dehydrated and crushed raw materials with aluminum chloride vapor at 600.degree. C.-900.degree. C., removing hot reaction gases containing iron chloride and titanium chloride, treating the residue with chlorine and a reducing agent, and processing the recovered aluminum chloride vapor containing silicon chloride and carbon monoxide at temperatures above 800.degree. C. with alumina or aluminiferous materials free from iron and titanium. The gases recovered from the chlorination process are oxidized to convert at least the chlorides of iron and titanium to their oxides prior to condensation. Therefore, because of the oxidation step, chlorides of the materials are not recovered in reusable form. Further, the vapor mixture recovered cannot be diluted with CO in order that the oxidation stage can be carried out.
Groth Column 1, lines 28 to 32 states:
Weston, U.S. Pat. No. 4,277,446, in the first chlorination stage, depends upon the use of excess aluminum chloride containing FeCl.sub.3 that is recovered from the circuit and returned to chlorinate the Fe.sub.2 O.sub.3. To quote, Column 8, lines 30-34
Most surprisingly I have found that with the present invention the removal of the Fe.sub.2 O.sub.3 from the raw material is far more effective than from either the teachings of Groth or Weston and in effect, as shown in the examples, has been reduced to a level which to the inventor's knowledge, has never been achieved heretofore by differential chlorination.